Eddy-current coupling



Nav. 23, 1943.

f FIGA.

EDDY-CURRENT' coI-JPLING Filed April 1s, i942 3 Sheets-Sheet 1 Nov. 23,1943.

M. P. wlNTHER EDDY-CURRENT coUPLING Filed April l16, 1942 :5sheets-sheetl s Patented Nov. 23, 1943 Martin P. Winther, Waukegan,Ill., assignor to Martin P. Winther, as trustee Application April 16,1942, Serial No. 439,205

15 Claims.

This invention relates to eddy-current couplings, and with regard tocertain more specific features to couplings of this' class which requirewater cooling. k

Among the several objects of the invention m-ay be noted the provisionof an effective cool'- ing arrangement particularly for large-sizedcouplings in which large amounts of power need to be dissipated at highslip rates; the provision of apparatus of the class described whichwilll perform its functions per se at relatively high eiliciency andwithout any substantial energy loss due to the use of the water; theprovision of apparatus of the classdescribed in which water is yprevented from entering the inner portions of the machine and in whichsaid inner portions may be additionally air-cooled; the provisionof amulti-coil arrangement which will prevent the formation of undesirablemagnetic circuits through the machine and which is conducive toefficient heat abstraction and also efficient use of copper in thecoils; the provision of apparatus of the class described which isrelatively quiet, and which if desired may be made dustandexplosion-proof. Other objects will be in part obvious and in partpointed out hereinafter.

The invention accordingly comprises the elements and combinations ofelements, features of construction, and arrangements of parts which willbe exemplified inthe structures hereinafter described, and the scope ofthe application of which will be indicated in the following claims.

In the accompanying drawings, in which is illustrated one of variouspossible embodiments of the invention,

Fig. 1 is a longitudinal cross section of a coupling embodying theinvention. being taken on line I-I ofFig'. 2;

Fig. 2 is a right-end elevation of Fig. 1;

Fig. 3 is a vertical section taken on line 3-3 of Fig. l; and,

Fig. 4 is a detail section of an air vent.

Similar reference characters indicate corresponding parts throughout theseveral views of the drawings.

In the development of eddy-current couplings or clutches, it has beenfound that there are a number of uses for units of very large size wherelargel powers need to be dissipated because of'the high' horsepowerrating of the clutch and be' cause'it is desirable to slip the clutchfor prolonged periods of time at high torques. Inasmuch as the problemof cooling` such couplings or clutches entirely by the use of air is a.difficult one, water cooling is preferable, and an improved the presentmachine.

- shaft 9 is a pilot bearing II.

method has been developed, as disclosed herein, for cooling such largerated machines by the use of water. A problem involved is that inapparatus of this class both the armature and the eld rotateindependently of each other, which introduces the necessity forpreventing water from entering the inner portions of the machine,butwithout using packing glands that are impractical in apparatus ofthis nature. This is particularly desirable Where additional air coolingis desired, as will appear.

Referring now more particularly to Fig. l, there is shown at numeral Ithe driven shaft of This driven shaft I is supported in part by abearing 3 in a stationary case 5.

The ycase 5 forms a frame and carries at its opposite end a bearing l inwhich is borne a drive shaft 9, to which is coupled the driver, usuallyan engine. Between the driven shaft I and the drive The drive shaft 9 isflanged as shown at I3 for accommodating said pilot bearing II and alsofor attachment at the left end, of a hollow armature drum I5.

Reference character I5 shows the drum in general. In particular itconsists of a left-hand head I'I (bolted to said flange I3) and arighthand head I9, which is carried on a pilot bearing 2I on themid-portion of the drive shaft I. Between the heads I1 and I9 is agenerally cylindric -body portion 23 provided with peripheraldepressions 25 land ridges 21. The inner surface 0f the cylinder 23 `iscylindrically smooth and the ends of said cylinder 23 are fastened andhermetically sealed to the heads I'I and I9.

Keyed tothe shaft I, .between the bearings II and 2|, is a eld member 29which is rotary with'salid4 shaft 2l. This field member 29 is formedwith teeth 3l on its edge which are parallel to its axis. It is alsoperipherally grooved at four points, as indicated at 33, for thereception respectively of four peripherally wound electric coils 35. Thecoils are energized by means of a'suitable circuit 31 closed betweenindependent slip rings 39 carried on and with the shaft I. The sliprings, 39 are fed current from suitable brushes 2.

The purpose of the teeth 3| on the iield member 29, as known, is toconcentrate the respective torio flux fields of the coils 35 forobtaining optimum conditions of eddy current in the drum I5. In thepresent case theseteeth also permit of the axial flow of air through thedrum I5 and around the member 29, as will appear.

Although in most eddy-current clutches built this is not as' desirableduring the early development of such equipment, it was customary to usea single coil, it has been found that, by using a number of coilsand'distributing the windings 'and the number of turns, an advantageis'obtained in the speed of application of torque developed by the fieldproduced by the coils, due to the reduction in inductance in the coils.For example, if all the coils are combined into one coil, the totalnumber ofturn's in the one coil would produce aivery'high inductance,considering also that allthe iron employed in the field magnetic circuitwould have to be Vconcentrated and associated with the single coil.`

-By using a multiple coil system, as shown, .the coils can be connectedin parallel or even if they are' connected in series, the higher voltageapplied reduces the inductance and therefore'the rate of asesoracylinder 23 is more conducive to spinning oif water than would be aperfectly cylindric exterior surface on the cylinder 23; and coolingwater is applied to this surface, as will be described.

Furthermore, the valley portions 25 of the undulations (between coils)bring cooling water as close as possible to the inner surface ofcylinder 23. -This reduces the average distance heat has time requiredto build up full flux in the circuit.

By the arrangement shown, it is possible to develop torque rapidlyinasmuch as the development of torque is a function of the applicationof flux to the air gap. This feature is of considerable importance in agreat many applications of the eddy-current clutch where rapidity of theapplication of the torque is desired. For example, applications havebeen encountered where a very large clutch, about 2000 H. P., requiredthe application of full torque during a period of less than 3 seconds,and then a release of such torque was required'over a period of 5 to 10seconds. Ordinarily, if a single coil were used, the vtime required tobuilt up theptorque would be 6 or 'l seconds, against less` thanl secondinthe case of the multi-coil arrangement.

As stated. the coils 35 may be wired in series or in parallel, accordingto design requirements. The coils should be wound so that thesurrounding toric fields indicated by the dotted 4lines P' produce northand lsouth polar conditions, such as indicated: that is, there should besimilar polarities at opposite ends of the field member 25 so that therewill not bea closed magnetic circuit through the heads, I 1, I9 andshaft I. Magnetization of shaft I has undesirable effects, including atendency to induce magnetism in connected equipment, and alsoa tendencyto attract metal particles. By having equal polarities at opposite endsof the held 25, no magnetic circuit is closed through the shaft I.

It will be seen that, with an even number of coils 35. the condition ofsimilar polarlties is obtained at the ends of the field member 25 andarmature drum I5, while atvthe same time adlaf cent sides of adjacentcoils have like polarities. It will be seen that, if an uneven number ofcoils were used and like polarities generated at the ends of the fieldmember and armature drum. unlike polaritieswould existlbe een coils, andas the ven-numbered condition. i 1

Also. this condition of an even number of coils preserves the toric fluxfield characteristics of each coil, since there i's noA bucking actionbetween the flux therebetween. 'Ihis makes desirable the wave form ofthe surface 25,21'0! the cylinder 23, with the high portions r ridges21.:

opposite the coils.-

The ridges 21 are opposite the coils 35 respectively, and the grooves 25are between. so that,

with a minimum weight in the inductive cylinderl 23, a proper crosssection is provided for flux passage. Inother words, the undulations 25,21 more or less follow the shapes or' pattern of 'the toric ilux fieldsgenerated bythe coils 35. I th l At the same time. this ridged surfaceto travel from the inner heat-generating regions of the cylinder 23.

The material of the field member 29 and oi the cylinder 23 is magnetic,land that of the latter should be as inductive as possible, so that theeddy currents set up therein bring about a magnetic reaction withrespect to the magnetic circuit around the coils 35 which causes themember 29 to be driven by the drum I5, thus electrically coupling theshafts I and 9. The amount of rotary slip between the shafts I and 9will depend upon the degree of energization of the coils 35. This isaccompanied by heating which increases as the slip increases.

To carry off the'heat engendered in the cylinder 23, water cooling ,isdesirable because of its high specific heat, compared to gaseous mediumssuch as air. On the other hand, to surround the cylinder 23 solidly withwater is conducive to undesirable energy loss because of friction andchurning, and is also conducive to leakage inward, which cannot easilybe controlled at the open bearing 2|, for example. Besides if aircooling of the field member 28 is desired, it would be difcult to havethe air traverse the centrally located water. An important pm of thepresent invention therefore comprises the elimination of thesedifficulties.

lalong the base a plurality of small water outlets 45. These wateroutlets 45 each provide a water spray upon the surface 0f the cylinder23. The rate at which water is sprayed upon this surface is not enoughto illl the space between the' drum I5 and the stationary case 5. Infact, the amount of water is relatively small and it is centrifugallyflung oil' from the surface 25, 21 against the inside of the case 5.

The lnsi le of the enclosing case 5 is baffled at intervals, asindicated at 51 (Fig. 3), from which the water defiects back upon therotating surface 25, 21. Thus the water is alternately moved from thesurface 25, 2-'I against the inner surface of 5, back and forthcontinuously, scrubbing as it goes, until it reaches .the bottom of thecase 5. The ridges 21 aid in whipping the water from the drum. At thebottom ofthe case is a water-receiving manifold 5 5, longitudinallyarranged and having an outlet II from which thewarm water flows bygravity. l i

In order that water may not by-pass the drain manifold 5l,` deilectorl58 are provided. These are oppositely sloped so'that one or the other isl effective. regardless oi' the direction of rotation of cylinder n.

From the above it Awill be seen that the space between the drum I5 andthe case 5 is not iilled between the parts I5 and 5. For example, the

volume of water is of the order of 5 to 10% of the total volume betweenthe drum I5 and case 5 down f ass-1,976

ai certain labyrinth seais ss, s1 which win be y mentioned. v

In order that `parts of the spray water may not be forced inward, anunpacked labyrinth is formed at. each end of the drum I5 by means of thetapered bead rings 55 interspaced between stationary tapered bead rings51 on the case 5. Thus if any spray water seeks to pass inward, it iseither promptly flung off centrifugally in a radial direction, or if itenters a labyrinth it is caught and feeds out over the tapers.

Since there is some tendency to form rings of water in the end regions59 of the-case 5, there are provided at the peripheries of these regions59 bailles BI which break up this ring and cause it to flow out throughlower manifold 49.

radiate heat inward against the coils and the member -29. This radiatedheat should be con ducted away from member 29, although its amountv isnot of the high order of the heat involved in the drum I5. It ispracticable to carry oil this heat with air. Air circulation within thedrum I5 and aroundfield member 29'is accomplishedby providing inletopenings 1I in thehead I9, and adjacent to these openings are outer fanblades 13. The blades draw in4 air through the openings 63 in the case 5and push it through the inlet openings 1I to the interior of the drumI5. This air is forced radially, as indicated by the' arrow, thencelongitudinally around the teeth 3I and outside ofthe coils 35. When itreaches the head I1 it flows inwardly and is pumped out through'openings 15 in said head I1 by means of inner fan blades 11, formed'within said head I1. This air circulation provides ample' coolingeffect for the interior radiation, thus protecting the eld member. Atthe same time, the interior of the machine including the coils 35 is notsubjected to any harmful effect of water, which is confined to coolingthe outsideof the drum Il.

Advantages of the invention are as follows:

The relatively small calculated amount of water used (Just enough tocarry off the heat), as compared to the old methods of using anexcessive over-supply of liquid coolant mass, avoids dynathe problem ofpreventing water from entering bearings such as 2i, and getting into theinside of the machine. In other'words, it is easier to centrifugallyhold oif from a bearing such as 2I by means of glands such as 55, v51,the small amounts of spray water involved; than it is to providepositive packingv means against a solid volume of water under staticpressure.v This is in addition to the point that such a solid mass ofwater engenders internal friction of turbulence which the spray waterdoes not.

Furthermore, without tight packing means air may be brought through thecase 5 and drum I5 to circulate between the drum I5 and the eld 29 asdescribed, for overcoming the radiant effects on the armature. Thiscouldnot be so readily 'accomplished if the problem needed to be faced ofhandling a solid volume of water between the drum I5 and the case 5.Also inflow of external air at 55, 51 aids in preventing outflow ofwater.

Regarding the dynamometer effect of any solid mass of water between thedrum I5 and the case 5, it may be appreciated that if the quantity ofthis water were appreciable the drum would be rotating in a cylinder ofwater, which it would tend to carry with it, and thus a great amount ofpower would be lost in the coupling. This is undesirable and the presentinvention avoids it.

The present machine also has advantages over 'machines in which air isalone depended upon for cooling the outside of the drum I5. With suchmachines,'the rate of air movement needs to be so large and it needs tobe so vigorous that excessive noise is ordinarily produced. This is nottrue of the present machine.

` It may be added that in the case of small designs of the presentmachine the interior air ventilation around member 29 may not benecessary. Thus the air vents 1I and 15 may be closed up, the fan blades23 and 11 eliminated and the labyrinths 55, 51 fitted closer. In suchcases the use of the spray cooling herein disclosed permits ofmanufacturing a dust-proof and explosionproof machine, where needed. Atthe same time the machine does not have the disadvantages of the lossesengendered by using large solid masses of water between the rotatingparts and the case.

It will be seen that, where internal air circulation is used, the hollowarmature drum acts as a conduit within which is the field member, andthat the fan members 23 and 11 act to draw air axially through openings1I, 15 in the ends of the drum. At the same time, the member 29 is.

- itself formed as a, diaphragm in the conduit rates `of heattransmission. By breaking up this which prevents air from by-pa'ssingstraight through the drum and spreads it'out to circulate between theedges of member 29 and the drum 23.

It is clear that, although the shaft 9 is shown as a. driver and shaft Ias a driven member, in some applications where the driven speed is nottoo low, the shaft I may be the driver and the shaft 9 the drivenmember. Otherwise the action the accompanying drawings shall beinterpreted as illustrative'and not in a limiting sense.

I claim:

l. In an electrical slip coupling, an enclosing case, a relativelymovable armature drum within the case, a relatively movable iield memberwith-f` in said armature drum, means for providing a iiux ileldinterlinking the ileld member and the i to throw outwardly any inwardlydirected water,

said case having an outlet for said water, the volume of water betweenthe drum and the case at any instant being substantially less than thevolunie between said Ydrum, the case and the labyrinth means, said casehaving axial openings communicating with the labyrinth means wherebyradial flow of air is induced through said labyrinth means, a reliefmeans in said case for preventing air pressure from building upexcessively from the inflow of air through the labyrinth means, saiddrum having axial openings, and bladed means associated with saidopenings for pumping air through the drum and around said field member,said air vpassing into and out of said case through the openingstherein, said air ilow being axial through the drum.

2. In an electrical slip coupling, an enclosing case, a relativelymovable armature drum within the case, a relatively movable field memberwithin said drum, means for providing a flux iield interlinking theiield member and the drum whereby eddy currents are engendered in thelatter and heat the same, means for spraying y water against the outsideof the drum in the space between it and the case, said case having anoutlet for said water, and water-deilecting means on the inner surfaceof said case for directing back to the drum any water thrown therefromcentrliugally.

V3. In an electrical slip coupling, an enclosing case, a relativelymovable and ridged armature drum-within the case, a' relatively movableileid memberithin said drum, means for providing a flux neldinterlinking the field member and the drum whereby eddy currents areengendered in the latter and heat the same, means for spraying a limitedamount of water against the outside of the drum in the space between itand the case, said case having'an outlet for said water,

and water-deflecting means on the inner surface of said case fordirecting back to the drum any water thrown centrifugally from itsridges.

4. In an electromagnetic slip coupling, a rotary ileld member, spacedux-forming coils formed around said ileld member, an armature drumsurrounding said field member, each o! said coils assaersf l I the fieldmember 'andthe'drmm aid drum havingf `alternate peripheral ridged andhollow portions forming a toric flux held interlinking the field lowportions therebetween.

5. In'an electromagnetic slip coupling, a rotary iield member, spacedilux-forming coils vformed around said member, an amature drumsurrounding said tleld member, each of saidfcoils forming an individualtoric ilux field interlinking on its exterior suriacegthe ridgedportions being opposite the respective coils in the adjacent fieldmember.

6. In an electromagnetic slip coupling, a rotary iield member, spacedilux-forming coils formed around said field member, an armature drumsurrounding said field member, each of said coils forming an individualtoric flux ileld interlinking the eld member and the drum, said drumhaving alternate peripheral ridged and hollow portions on its exteriorsurface, the ridged portions being opposite the respective coils in theadjacent field member, and means for spraying water on the exterior ofsaid drum to be spun oil' from said ridged portions.

'7. In an electromagnetic coupling, an enclosing case, a rotary hollowarmature drum, a rotary eld member within said drum, spaced peripheralfield coils at the edge of the iield member, means forenergizing saidcoils to provide toric flux ilelds interlinking the field member and thedrum, said drum having external ridges adjacent the respective fieldcoils on the eld member with depressions therebetween, and meansassociated with the case for spraying liquid upon the ridged surface ofsaid drum without iilling the space between the/drum and the case withsaid liquid.

y 8. In an electromagnetic coupling, an enclosing case, a rotary hollowarmature drum, a rotary iield member within said drum, spaced peripheraleld coils at the'edge of the eld member, means for energizing said coilsto provide toric iiux fields interlinking the ileld member and the drum,said drum having external ridges adjacent the respective eld coils onthe field member with depressions therebetween, and means associatedwith the case for spraying liquid upon the ridged surface of said drumwithout lining the space between the drum and the case with said liquid,the current in said ileld coils being such that the endwise polarity ofthe field member and drum are the same.

9. In an electromagnetic coupling, an enclosing case, a rotary hollowarmature drum, a rotary neld member within said drum, spaced peripheraleld coils at the edge of the eld member, means for energizing said coilsto provide toric ilux elds interlinking the field member-and thearmature drum, said drum having external ridges 'adjacent the respectiveiield coils on the iield member with depressions therebetween, and meansassociated with :the case for spraying liquid upon theridged surface ofsaid drum without lling the space between the drum and the case withsaid liquid, connections causing the current in said ileld coils beingsuch that the endwise polarity of the neld member and drum are the same,and causing the same polarity to exist between adjacent surfaces ofadjacent coils, the number of coils being even.

10. In an electrical slip coupling, an enclos- I ing' case, 'arelatively movable armature drum within the case, a relatively movableiield mem- Der within said armature drum, means for providing a iluxileld interlinking the field member andthe armature drum whereby eddycurrents are engendered. in the latter to heat the same, means forspraying water. aga-inst the outside of the drum in the space between it'and the case, annular packless labyrinth means between the ends of theinductor drum and the case adapted centrirugally to throw outwardlyanyinwardly dlcase, a relatively movable, water-cooled armaturedrum withinthe case, annular labyrinth packing means between theV drum and case, arelatively movable field member within said armature drum, means forproviding a flux eld interlinking the field member and the armature drumwhereby eddy currents are engendered in the latter to heat the same, theperipheral surface of the field member being recessed to provide fluxconcentrating means and intermediate spaces for air flow, said case anddrum having axial openings within the periphery of the packing means,and bladed means associated with the said opening in the drum forpumping air through the case and the drum and around said field member,the field member being mounted so as substantially to form anair-blocking diaphragm across the drum and forcing said iiow to takeplace first radially outward from within one packing to the periphery ofthe field member, then axially between the recessed periphery' of thefield member and the drum, and finally radially inward and out throughthe other packing means. i

12. In an electrical slip coupling, an enclosing case, a relativelymovable armature drum within the case, a relatively movable field memberwith.

in said armature drum, means forv providing a ux field interlinking thefield member and the armature drum whereby eddy currents are' engendered.in the4 latter vto heat the same, said drum having axial openings,`andbladed means associated with said openings for pumping air through thedrum and around said field member, said air passing into and out of saidcase through the openings therein, said air flow being through the drum,the field member being mounted so as substantially to form anair-bioching diaphragm and forcing said axial ilow to take place betweenthe periphery of the field member and the drum.

, 13. In an electromagnetic slip coupling, a ro- 5 tary field member,spaced iiux-'forming coils formed around said member, an armature drumsurrounding said field member, electric connections to said coilswhereby individual'toric ilux fields are formed interlinking the fieldmeml0 ber and the drum with like polarities of magnetic flux betweenadjacent coil parts, said drum having alternate peripheral heavier andlighter portions on its exterior surface, the heavier portions beingsubstantially in the planes of said coils '15. of the eld member and thelighter portions being substantially` between the planes between thecoils.

. 14. In an electromagnetic slip coupling, a rotary field member, spacedAflux-forming coils formed around said member, a rotary armatureAdrumsurrounding saidfield member, electric connections to said coilswhereby individual toric flux fields are formed interlinking the iieldmember and the drum with like polarities of magnetic V2:5 iiux betweenadjacent coilparts, said drum externally having alternate vperipheralheavier ridges and lighter peripheral valleys, the ridges beingsubstantially in the planes of said coils of the'eid member and thevalley portions being substantially in the planes between the coils; andmeans for supplying water on the exterior of the drum, said ridgesandvalleys functioning i electrically to form an' adequate flux pathwithout excess thicknessesfor the purpose and the ridges .35 underrotation being adapted to spin off water from the drum. v

15. In an electromagnetic slip coupling, a rotary field member, spacedflux-forming coils formed around said member, a rotary armature y 40drum surrounding said field member, electric' connections to said coilswhereby individual toric ilux fields are formed interiinking the fieldmember and the drum with like polarities of magnetic iiux betweenadjacent coil parts, whereby a magv netic field is formed in the drumhaving an externally cylindric ridged pattern; said drum hav- 4 ing abasic externally spaced peripheral ridge and groove form substantiallyfollowing thepattem Y engendered by said magnetic-field.

P. WINTHER.

